In the annals of wrongful convictions, there is nothing that comes close in size to the epic drug-lab scandal that is entering its dramatic final act in Massachusetts.

About 23,000 people convicted of low-level drug crimes are expected to have their cases wiped away next month en masse, the result of a five-year court fight over the work of a rogue chemist.

“It’s absolutely stunning. I have never seen anything like it,” said Suzanne Bell, a professor at West Virginia University who serves on the National Commission of Forensic Science. “It’s unbelievable to me that it could have even happened. And then when you look at the scope of the number of cases that may be dismissed or vacated, there are no words for it.”